A Porsche Cayenne for diesel fetishists only

DanNeil

The diesel-powered 2013 Porsche Cayenne SUV.

In my continuing war on U.S. customary units of weights and measures, I would like to point out that, on Porsche’s U.S. website, the fuel-injection pressure of the Cayenne Diesel is listed as 29,007 pounds per square inch

Really? Is that the number the people at Robert Bosch had in mind when they were modeling the V6’s common-rail, direct-injection fuel system? Yah, neunundzwanzig tausend…und sieben! Why don’t we join the civilized world and call that 200 megapascals, or the elegantly convertible 2,000 bar? What’s with the drams per hectare?

Metric, people. Get with the program.

This is the second near-six-figure, diesel-powered Panzer featured here in two weeks, after the Mercedes-Benz GL350 BlueTec. And it won’t be the last, as I expect Audi to kindly send me its new Q7 diesel SUV, VW its Touareg V6 TDI and BMW its new diesel-powered X5 xDrive35d, which sounds like it was named by Langley.

The diesel segment in America is essentially German air space, with Mercedes, BMW and the Volkswagen Group cohort of Audi, VW brand and Porsche
POAHY, -1.89%
responsible for nearly all the offerings, about two dozen, not counting trucks. This year’s crop of U.S.-spec oil-burners has among them a car I absolutely covet: the BMW 35d Sport Wagon with a turbodiesel six. Give me that all-wheel drive, too, Mr. Car Salesman. That is so nasty!

Yes, the Germans have jumped in with both feet, and they have been rewarded with pretty flat demand, actually. Diesel market penetration in the U.S. hovers around 3%, and while sales of diesels are up 27% in the first half of 2012, according to the Diesel Technology Forum, they’re up from a very small number.

Why is demand flat? One reason is the stubborn price premium on diesel fuel, which was running 15% higher than regular gasoline—a whopping 60 cents per gallon—in the last week in November, according to the U.S. Energy Information Administration. Whatever mileage advantages diesel vehicles offer are being largely zeroed out at the pump.

The vehicles themselves carry a diesel penalty. The base price of our test car this week, an outrageously well-made 2013 Porsche Cayenne Diesel, is $3,900 higher than that of the comparably equipped base model with a gasoline six and Tiptronic automatic transmission. I’ve just run some numbers: In order to recoup, in fuel savings, the additional outlay for the Cayenne Diesel you would have to own it for about 11.9 years. May I suggest an air freshener?

Also, to comply with prevailing U.S. emissions standards on nitrogen oxides, or NOx, these big diesels require fairly complicated systems of postcombustion treatment with a water-based urea solution, called AdBlue. Injected into the exhaust stream, the solution’s ammonia reacts in the de-NOx catalyzer to form nitrogen and water vapor.

Not exactly carefree motoring

It’s all very top-flight chemistry, but not exactly carefree motoring. Topping off the Cayenne’s 22-liter AdBlue reservoir is part of the regular service schedule, but it’s entirely possible to run out of the stuff between services, depending on how you drive. Exhausting the AdBlue will immobilize the vehicle. The solution itself is cheap—under $50 from retailers and truck stops—but refilling the AdBlue yourself can be a little tricky, as ideally you’d want to evacuate the remaining solution from the tank before refilling. In any event, the AdBlue constitutes just one more gauge for owners to eye warily.

Another compromise has to do with the full-size spare tire, which goes missing in the Cayenne Diesel, displaced by the AdBlue reservoir (diesel models get a space-saver spare).

Diesel advocates love to push the cost-of-ownership pencil, but I’m here to tell you, in the case of the Cayenne Diesel, the economics are horrible and unsubtle. Not to mention that the diesel weighs 320 pounds more than the base gas-powered Cayenne Tiptronic. We are talking about a vehicle—a Porsche, no less—with a weight-to-power ratio of about 20 pounds per horsepower (4,795 lbs./240 hp), almost exactly that of a Hyundai Veloster. With 406 pound-feet of torque and eight forward gears, the diesel chortles and snorts to 60 mph in 7.2 seconds, a couple of ticks quicker than the V6. The diesel will certainly barrel up an on-ramp well enough. The upshifts whisper, barely detectable in the midst of a very refined full-throttle commotion. Engine elasticity is reasonable. Porsche lists the 50-to-75-mph acceleration at 5.3 seconds. But above those speeds, the diesel’s throttle response becomes deeply measured and wafting, never punchy nor particularly fun.

Towing rating is the same for both V6 and diesel: 7,716 pounds, with a braked trailer.

Like all other Cayennes, the Diesel has tight, well-sorted, premium German handling. The chassis is insanely rigid, and the suspension (double wishbones in front, multilinks in back) strikes an excellent balance of ride compliance and cornering composure. The steering is responsive on-center going straight ahead and nicely weighted and precise while cornering. Our test vehicle had the optional air suspension ($3,980) as well as the staggering 21-inch alloy rims and sport tires. Torque-vectoring all-wheel drive, adaptive air suspension, 18-way adaptive sport seats. All told, a lot to love, for a mere $37,000 or so over the base price.

The real question

The point is that, performance-wise, the Cayenne Diesel isn’t wildly better, or worse, than the version with the gasoline V6. So, if the performance is a draw and the economics disadvantage the diesel, the real question is: Why would anyone want the Cayenne Diesel?

It’s because diesel is a car geek’s fetish. Take the range thing: The Cayenne Diesel’s one towering superlative over the gas V6 model is its highway range, 765 miles, give or take a small state. I’m pretty sure I could cross the country with only two fuel stops. And I must say there’s some illicit thrill in watching what appears to be a stuck fuel gauge for days on end.

But it’s meaningless, an irrelevant benchmark, a number without consequence. Are you planning to drive for 14 hours straight? When are you going to empty your own reservoir?

There’s also the whole Gesamtkunstwerk of diesels, the reassuring, steady throb of the engine, the masculine, heavy-duty cackle, heavily muted, like an agrarian race memory. It’s one thing to go fast in a tightly strung, gas-powered vehicle. Going fast in a diesel is a different and strangely larger-bore experience. I can understand why some contrarians might prefer it.

My biggest problem with the Cayenne Diesel is its provenance. I think a diesel SUV with 240 hp, sharing its powertrain in most respects with corporate cousins Audi Q7 and VW Touareg TDI, is below the line for Porsche, brand-wise. Such a vehicle lacks authenticity, and the performance lacks the minimal frisson one must associate with Porsche. In its quest to become the world’s largest car company, VW Group must not allow Porsche to be drawn into the badge-engineering vortex.

As to whether any of that should matter to you, please consult your own conversion tables.

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